Overload protective means



June 6, 1944.

V L. s. WALLE OVERLOAD PROTECTIVE MEANS Original Filed Dec. 12. 1959INSULATION .6 w :a .n W w 4 ts & mg .A Cs v u switch in its open circuitposition.

7 transformer.

Reissuejd June 6, 1944 OVERLOAD PROTECTIVE MEAN Ludwig S. Walle,Lansdowne, Pa., assignor to General Electric Company,

York

a corporation of New Original No. 2,268,229, dated December 30, 1941,

Serial No. 308,785, December 12, 1939. Application for reissue November25, 1942, Serial No.

15 Claims.

My invention relates to overload protective means, more particularly toprotective devices 'for electric energy. translating apparatus of the-oil immersed type Such as transformers, and has for its object asimple, reliable and inexpensive protective device of this type.

My invention is especially useful in distribution transformers which aremounted in convenient but isolated positions in the distributionneltwork and are inspected at infrequent interva s.

'In carrying out my invention, I provide a pro tective device consistingof a thermally operable snap acting switching means which is connectedin the secondary circuit of the transformer and immersed in thetransformer oil so as to be responsive to the oil temperature. I alsoprovide a latching means for holding the switching means in its opencircuit position after it has opened and closed a plurality of timeswithin a predetermined range. This latching means is operated .by asecond temperature responsive means inresponse to the current in thesecondary circuit or to the oil in which it is immersed so as to movethe latching means to hold the I also provide manually operated meansoperable from the exterior of the transformer casing for opening andclosing the switching means.

For a more complete understanding of my invention, reference should behad to the accompanying drawing showing a protective device embodying myinvention applied to a transformer, while Fig. 2 is a front elevationview of the bimetallic snap operating means.

Referring to the drawing, I have provided overload protectivemeanscomprising in the form shown a snap action bimetallic thermostat .H]which constitutes a bridging switching member in the circuit of thesecondary winding ll of a This thermostat III has a substantiallyrectangular body portion which is supported at its center on a pin orpost l2 secured to an insulating support I3 made of a suitableelectrically insulating material such as slate.

The main rectangular portion of the thermostat has a concavo-convex formfor the purpose of giving it a snap action. When the thermostat Is inposition to close the secondary circuit of the secondary winding II, asshown in the drawin the side of the thermostat adjacent the support J3isconcave. Upon an increase in temperature ofthe thermostat to apredetermined value, the

unequal expansion of its two metals, the metal having the greatercoefficient of expansion being adjacent the support [3, causes it tosnap at some predetermined temperature to reverse its shape as indicatedby the dotted line position M. The

side of the thermostat adjacent the support 13 is then convex. When thetemperature of the thermostat drops to a predetermined point, thethermostat resumes the shape indicated in the drawing with a snapaction.

As shown; the rectangular portion of the thermostat is provided at itsopposite ends with central extensions l5 and I6 to which are securedelectric switch contacts I5a and Na respectively. These contactscooperate with stationary contacts l1 and i8 secured to the support l3.Preferably, as shown, the stationary contacts are mounted on bolts orlugs which extend through the base and are clamped to the base by meansof suitable nuts. The opposite ends of the bolts form connectionterminals I9 and 20 for connection of the protective device includingthe thermostat In in circuit with the secondary Winding H.

The extension I6 extends downward below the contact Ilia and is benttoward the right-hand as seen in Fig. 1 ofthe drawing to form alatchrelation therewith to the bolt or post 24 forming the support forthe stationary contact l8. To facilitate a good thermal contact, thepost may be made in two parts secured together by a screw connection 25so as to clamp the end of the thermostat 23 between the two parts.

Moreover, the bolt or post 24 has an electrical resistance such that ithas substantially the same thermal characteristics as the transformersecondary winding H and primary winding 26. In other words, heat isgenerated in the bolt 24 by the current passing through it at such. ratethat the temperature rise of the bolt follows the temperature rise, andalso temperature decrease, of the transformer windings. Preferably, topromote this temperature rise in the bolt, it is surrounded by a heatinsulating jacket 24a made of a suitable heat and electricallyinsulating material such as fiber. This heat insulating jacket preventsthe rapid cooling of the bolt by the surrounding'oil 21 in thetransformer.

This heat generated in the bolt 24 raises its temperature above thetemperature of the surrounding oil and the heat is transferred by coduction toth'e thermostat 23. Also the oil itse f,

particularly on light over-currents, is heated by the windings andapproximates the temperature of the windings. The oil will also havesome effeet on the heating of the thermostat 23. As the temperature ofthe thermostat 23 rises, its distortion moves the insulating latch 22upward, as seen in Fig. 1, until finally the latch is in a position toengage the projection 2| and prevent the return snap action of thethermostat ID to its closed circuit position, shown in the drawing.During the time that the thermostat 23 is being heated, the thermostatIll will have been heated to snap to its open position and then cooledto snap to its closed position, several times.

In the operation. of the transformer, the secondary current flowingthrough the thermostat Ill heats the thermostat. Also heat is impartedto the thermostat by the cooling fluid, shown as the oil 21 in which thetwo thermostats and the transformer windings are immersed. Upon theoccurrence of a substantial overload current in the secondary windingthe thermostat Illv is heated to a temperature causing it to snap to thereverse position indicated by dotted lines and therebyopen the secondarycircuit; It is contemplated that the temperature of the thermostat undersuch conditions will be considerably above the temperature of the oil inwhich it 'is Consequently, the thermostat is I immersed. cooled rapidlyby the oil and snaps to reclose the circuit after remaining in its opencircuit position a short interval such as a few seconds.

This overload current, however, likewise heats the thermostat 23although the response of the thermostat 23 is slower, it being heated aspreviously noted at a rate approximately the rate of heating of thetransformer windings. Its temperature, however, is somewhat higher withsubstantial overloads than the temperature of the surrouning oil. Whenthe thermostat II) has opened and closed the circuit a number of times,such as five Or more, the thermostat 23 will have moved the projection23 to a latching position in which it holds the thermostat III in itsopen r circuit position.

Of course the rate at which the thermostats are heated will depend uponthe current in the secondary winding. The thermostat ID will be adjustedor constructed ordinarily to open and opening and closing operations aswith the predetermined current value.

The plurality of reclosing operations provides for the resumption ofservice in the event that the excessively heavy load is removed duringthe opening and closing circuit interval. If the heavy overloadpersists, thenthe circuit is permanently latched open.

Moreover the thermostat I0 is constructed a d arranged to'remain open inresponse to a predetermined temperature which is the maximum permissibletemperature of the oil. This temperature is not high enough to cause thethermostat to snap open, but it is high enough to cause it to remainopen afterit has snapped open,

i. e., high enough to prevent reclosure of the thermostat. In the eventthat the oil reaches this temperature because of continued lightoverloads the thermostat Ill remains open until the oil cools regardlessof whether it is secured open by the latch 22. Preferably this maximumoil temporature is not high enough, however, to cause the thermostat 23to move the 1atch into an engaging position. It will thus be observedthat during these persisent predetermined light overloads the thermostat||l opens and closes the circuit an indefinite number of times,remaining open [or relatively long time intervals, and is not finallylatched open by the thermostat 23. The arcs generated by the opening ofthe circuit heat the oil and contribute in the raising of the oiltemperature to the maximum value.

I have also provided manual means for bodily mov ng the thermostat Hi toits open and closed positions. This consists of an arm 28 inside thetransformer tank 29 having its free end opposite the inner end of a rod30 carrying the thermostat ID. The upper end of the arm 28 is pivoted ona shaft 3| which extends through the wall of the tank and has secured toit an ex terior operating arm 32. On the end of the arm 32 is a link 33through which the hook of an operating pole may be inserted to move thearm 32 downward andopen the circuit. It iscontemplated that the weightof the operating pole on the arm 32 will be sufficient to hold thethermostat ID in its open circuit position.

As shown, the rod 30 extends through an aperture provided for it in thebase 13, the post |2 constituting a flange secured to the rod 30, and

also through an aperture in the thermostat Ill.

The left-hand end of the rod 30 is threaded and provided with anadjustment nut 34 bearing on a helical spring 35 which, in turn,'pressesagainst a collar 36 on the rod 3|). This collar engages the thermostat I0 and holds it against the flange l2, or ina predetermined adjustedrelation with the flange l2. A second spring 31 surrounding the oppositeend of the rod 30 biases the rod in a right'ehand direction. It will beunderstood that the springs '35 and 31 are strong enough to maintain thedesired contact pressure and overpower substantially the thermostat Ill.

When the latch 22 engages the projection 2|,

thethermostat Ill is held in its open circuit position regardless of,the temperature to which it subsequently cools. The released thethermostat Hi from the latch 22 is a manual operation whereby thethermostat I ll is moved bodily toward the left.- It is carried out bypulling downward on the lever 32 to move thereby the supporting rod 30and the thermostat l0 toward the left, as seen in the drawing, farenough to disengage the projection 2| from the latch. This manualrelease operation has of course the pre-' contacts in circuit with anenergy translating,-

man! modifications may be made and I, therefore, contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent in the UnitedStates is:

1. A protective device for a translating device immersed in oilcomprising a bimetallic thermostat arranged to snap from one position toanother in response to changes in temperature thereof, said thermostatbeing arranged to be immersed in the oil with the translating device soas to be responsive to the temperature of the oil, circuit control meansactuated by said thermostat, said circuit control means being connectedin a circuit of the translating device and being normally in a closedcircuit position, connections for heating said thermostat in response tothe current in said circuit, a second thermostat, latchin means actuatedby said second thermostat in response to a predetermined temperature ofsaid second thermostat for holding said said first thermostat in itsopen circuit position, and means for manually moving said firstthermostat to release it from said latching means.

2. A protective device comprising temperature responsive operating meansarranged to move from one position to another position and backin itsopen circuit position, and connections for heating said second operatingmean in response to the current in said control means, said firstoperating means being heated to its operating temperature before saidsecond operatin means is heated to its operating temperature so thatsaid first operating means operates said circuit control means aplurality of time before said second operating means moves said holdingmeansto hold said first operating means in its open circuit position.

3. A protective device comprising a bimetallic thermostat arranged tosnap from one position to another in response to changes in temperaturethereof, circuit control means actuated by said thermostat betweenclosed and open circuit positions, said circuit control means beingnormally in a closed circuit position, connections for heating saidthermostat in response -to the current in said control means, a secondthermostat, stop means actuated by said second thermostat when heated toa predetermined temperature to hold said first thermostat in its opencircuit position, and connections for heating said second thermostat inresponse to the current in said control means, said first thermostatbeing heated to its operating temperature before said second thermostatis heated to its operating temperature so that said first thermostatoperates said circu t control means a plurality of times before saidsecond thermostat moves said stop means to hold said first thermostat inits open circuit position.

4. A protective device comprising a pair of stationary contacts, meansfor connectin said device, a bimetallic thermostat provided with spacedmovable contacts engaging said stationary contacts to close a circuitthrough said thermostat, said thermostat being heated by the currentpassing through it and arranged when heated to a predeterminedtemperature to snap to another position and thereby move said movablecontacts to open said circuit, a second thermostat having one endmovable in response to changes in temperature, -a latchingmember carriedby the movable end of saidsecond thermostat, means for heating saidsecond thermostat in response to the current in said circuit at a ratesubstantially the same as the rate of heating of the translating devicewhereby said second thermostat moves said latching member in response toa predetermined maximum temperature to a position to hold said firstthermostat in its open circuit position, said first thermostat beingheated to its operating temperature before said second thermostat isheated to its operating temperature, and said first thermostat operatingto open and close the circuit a plurality of times before 'said secondthermostat moves said latching member to a position to hold said firstthermostat in its open circuit position, and manually operated means formoving said first thermostat bodily to open said circuit.

5. A protective device for an electric translating device immersed in acooling fluid, said device being arranged to be immersed in the coolingfluid with the translating device, comprising switching means arrangedto be connected in a circuit of the translating device, temperatureresponsive operating means connected to said cuit position when thetemperature of said operating means is below a predetermined temperatureand to move said switching means to an open circuit position when thetemperature of said operating means is above said predeterminedtemperature, connections for heating said operating means in response tothe current'in a circuit of the translating device, and means formanually moving said temperature responsive means to open and close saidswitching means.

6. A protective device for an electric translating device immersed inoil, said device being arranged to be immersed in the oil with thetranslating device, comprising switching means arranged to be connectedin a circuit of the translating device, temperature responsive operatingmeans connected to said switching means so as to open and close saidswitching means in response to changes in the temperature of the'oil andarranged to maintain said switching means in a closed circuit positionwhen the temperature of said operating means is below a predeterminedtemperature and to move said switching'means to an open circuit positionwhen the temperature of said operating means is above said predeterminedtemperature, connections for heating said operating means in response tothe current in a circuit of the translating device, a second temperatureresponsive operating means, means actuated by said second operatingmeans in response to a predetermined temperature for holding said firstoperating means in its open circuit position, and connections forheating said second operating means in response to the current in acircuit of the translating device.

7. A protective device for an electric translating device immersed inoil, said device being arranged to be immersed in the oil with thetranslating device, comprising switching means arranged to be connectedin a circuit of the translating device, temperature responsive operatingmeans connected to said switching means so as to open and close saidswitching means in response to changes in the temperature of the oil andarranged to maintain said switching means in a closed .circuit positionwhen the tempe ature of said operating means is below a predeterminedtemperature and to move said switching means to an open circuit positionwhen the temperature of said operating means is above said predeterminedtemperature, connections for heating said operating means in response tothe current in a circuit of the translating device, temperatureresponsive latching means for holding'said operating means in its opencircuit position, and manually operated means for releasing saidoperating means from said latching means.

position to another in response to changes in its temperature whenimmersed in thecooling fluid,

circuit control means arranged for connection in a circuit of thetranslating device. actuated by said thermostat between closed and opencircuit positions, said circuit control means being nor- 7 mally in aclosed circuit position, connections for heating said thermostat inresponse to the current in a circuit of said translating device,

a second thermostat, latch means actuated by 7 said second thermostat inresponse to a predetermined operating temperature to hold said firstthermostat in its open circuit position, and

connections for heating said second thermostatin response to the currentin a circuit of said translating device, said first thermostat being,

' ates to open and close said circuit control means a plurality of timesbefore said second thermostat moves said latch means to hold said firstthermostat in its open circuit position.

9. A protective device for an electric translating device immersed inoil, said devicebeing arranged to be immersed in the oil with thetranslating device, comprising switching means arranged to be connectedin a circuit of the translating device, temperature responsive operatingmeans connected to said switching means so as to. open and close saidswitching means in response to changes in the temperature of the oil andarranged to maintain said switching means in a closed circuit positionwhen the term perature of said operating means is below a predeterminedtemperature and to move said switching means to an open circuit positionwhen the temperature of said operating means is above said predeterminedtemperature, connections for heating said operating means in response tothe current in the circuit of the translating device so -as to causesaid operating means to open and the translating device, a latchoperable by said switching means after relatively long time intervals inresponse to a current in the circuit-of the translating device of apredetermined low value, and a second temperature responsive operatingmeans for holding said first temperature responsive operatingmeans inits open circuit position after a plurality of said short time intervaloperations.

10. A protective device for an electric translating device immersed in acooling fluid, said device being arranged to be immersed in the coolingfluid with the translating device, comprising switching means arrangedto be connected in a circuit of the translating device, temperatureresponsive operating means connected to said switching means so as toopen and close said switching means in response to changes in thetemperature of the cooling fluid and arranged to maintain said switchingmeans in a closed circuit position when the temperature of saidoperating means is below a predetermined temperature and to move saidswitchingmeans to an-open circuit position when the temperature of saidoperating meansis above said predetermined temperature, connections forheating said operating means in response to the current in the circuitof the translating device so as to cause said operating means to openand close said switching means after relatively short time intervals inresponse to a current in the circuit of the translating device of apredetermined high value and to open and close said switching meansafter relatively long time intervals in response to a current in thecircuit of the translating device'of a predetermined low value, a secondtemperature responsive operating means arranged to be immersed in thecooling fluid with second operating means to a position to hold saidfirst temperature responsive operating means in its open circuitposition and means for heating said second" temperature responsiveoperating means in response to the current in a circuit of thetranslating device to cause said I, second operating means to move saidlatch to said latching position after a plurality of said short timeinterval operations of said. first operating means.

11. A circuit breaker comprising a first con-- tact, a thermallyresponsive snap acting bimetal element carrying a second contact forengaging said first contact, an operating handle mounted solely forpivotal movement on a fixed pivot,

element for engaging said first contact; an operating spring engaging astationary support at one end and actingat all times to bias one of saidcontacts in one direction, manually movable operating means operable tocause opening or closing of said contacts, said operating spring beingfree of connection with said manual operating means, said bimetalelement when heated a predetermined amount operating to cause automaticopening of said contacts irrespective of the tion of said manualoperating means.

posihaving a normal concave-convex flexed position,

a pair of said element adjacent the edge thereof and extending outwardlytherefrom on opposite sides, a

pair of movablecontacts mounted on the-flexed ends of said arms forengaging said sta onary contacts, a manual operating member for movingsaid element to manually open or close the contacts, said bimetalelement when heated a predetermined amount by overload current operatingto snap from its normal flexed position to an opposite concavo-convexposition thereby automatically to open the contacts irrespective of theposition of said manual operating member.

14. A'circuit breaker comprising a stationary contact, a snap-actingbimetallic element having a normal concavo-convex flexed position, amovable contact carried by said element for cooperation with said fixedcontact, a manual operating member for moving said element to manuallysaid contacts, said bimetallic eleopen or close arms of conductingmaterial secured to.

meat when heated a predetermined amount by overload current operating tosnap from said normal flexed position to an opposite concavoconvexposition thereby automatically to open the contacts irrespective of theposition of said manual operating member.

15. A circuit breaker comprising a stationary contact, a movably mountedsnap-acting bimetallic element having a normal concavo-convex flexedposition, a movable contact carried by said bimetallic element forcooperation with said fixed contact, means for biasing said bimetallicelement for movement to a first circuit controlling position, and amanually operable member for moving said element to a second circuitcontrolling position,'said bimetallic element when heated a predetermined amount by overload current operating to snap from said normalflexed position to an opposite concavo-convex position thereby automatically to open the contacts irrespective of the position of saidmanually operable member.

LUDWIG S. WALLE.

